1. Field of the Invention
The present invention relates to machines that require high DC currents to be distributed over significant distances to multiple high current loads. More particularly, the present invention relates to an economical DC current distribution method and apparatus for use with electronic devices having fairly constant and well defined DC current requirements and that do not exhibit large dynamic variation or that are substantially buffered by capacitors at each load.
2. Description of Related Art
The use of an AC to DC converter or DC to DC converter at each load is a known way to provide for distributing DC power to each load without the negative effects of resistive voltage drop and ground shift as is experienced in a simple metal conductor distribution system. Each converter acts as a power supply for its' load. This approach is expensive in that numerous complex power control circuits are required in the system. It becomes even more expensive when redundancy is required to be built into the distribution system since a redundant supply or converter is needed for each load. Also when the power distribution system becomes large, distributed converters must be placed at intervals of several meters along a cable of ten meters or more. Such placement often presents a problem of instability and noise in the paralleling circuits and sensing circuits.
U.S. Pat. No. 5,319,536 issued to Malik, is an example of paralleling in which three converters, 11, 13 and 15 are connected in parallel to load 23.
U.S. Pat. No. 5,500,791 issued to Kheraluwala et al. teaches solving these problems by providing a dual active bridge converter generating 100,000 Hertz AC power square wave output which can be converted to DC by a converter at each load. The converters of Kheraluwala need not have such massive magnetic paths as would be required by a 60 Hertz system but there is still the need for a transformer, rectifier and possibly a voltage regulator at each load.
U.S. Pat. No. 5,254,877 issued to Tice et al. is another example of additional active power supply units being added along a distribution line. In Tice et al. a control panel provides power and communicates with smoke detectors and intrusion detectors. The line conductors 14a and 14b of Tice et al. serve as both signaling lines and power distribution lines and as is usual, the detectors farthest from the control panel would receive attenuated power levels. Tice et al. overcome this attenuation by providing distributed power supplies with synchronizing circuits, the added power supplies sense and respond to power pulses from the main control panel to inject supplemental amounts of power into the line during the power distribution time intervals. These added power supplies are relatively costly and they themselves require an external source of power such as from a AC power receptacle.
U.S. Pat. No. 5,777,276 issued to Zhu describes distribution of power on a computer motherboard using an auxiliary conductor system to reduce voltage loss due to high currents through resistive areas in the contact regions between connector posts and conductive layers buried in the motherboard. In the motherboard of Zhu, the conductors themselves are considered to have negligible resistive losses which of course is not the case in machines having larger distribution distances. The teachings of Zhu do not account for voltage loss in the original conductor or the auxiliary conductor and therefore his teachings do not concern voltage variations as a function of distance.
U.S. Pat. No. 4,788,449 issued to Katz describes a matrix of loads being supplied by a column of power supplies and redundantly by a row of power supplies. Although this teaching may solve a problem of the prior art with a short circuit in one load causing failure of power to all others in the same row, this teaching does not solve the problem of DC power attenuation at the farthest most load such as load 15 for example
The present invention overcomes these inadequacies, problems and disadvantages of the prior art by means of the apparatus and method of the invention which is summarized below.